Carotenoids are structurally diverse pigments with various important biological functions. There has been a large interest in the search for novel carotenoid structures, since only a slight structural changes can result in a drastic difference in their biological functions. Carotenoid-modifying enzymes show remarkable substrate promiscuity, allowing rapid access to a vast set of novel carotenoids by combinatorial biosynthesis. We previously constructed a nonnatural carotenoid biosynthetic pathway in Escherichia coli that can produce C50 carotenoids having a longer chain than their natural C40 counterparts. In this study, a carotenoid 2,2'-hydroxylase (crtG) from Brevundimonas sp. SD212 was coexpressed together with our laboratory-engineered C50-zeaxanthin and C50-astaxanthin biosynthetic pathways. We identified six novel nonnatural C50-xanthophylls, namely, C50-nostoxanthin, C50-caloxanthin, C50-adonixanthin, C50-4-ketonostoxanthin, C50-2-hydroxyastaxanthin, and C50-2,2′-dihydroxyastaxanthin.
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